1. Field of the Invention
The present invention relates to a method and apparatus for detecting foreign matter attached to a peripheral edge of a substrate, as well as a storage medium, and in particular to a method and apparatus for detecting foreign matter attached to a peripheral edge of a substrate, which detects foreign matter such as a polymer attached to a peripheral edge of a substrate by carrying out preliminary processing to emphasize the foreign matter and then checking the peripheral edge of the substrate, as well as a storage medium.
2. Description of the Related Art
There may be cases where a polymer as foreign matter becomes attached to an edge face and its surrounding oblique portion (hereinafter referred to as a “peripheral edge” or “bevel portion”) of, for example, a wafer as a semiconductor substrate that has been subjected to etching processing and so on, and in general, such a polymer is called a bevel polymer. For example, the bevel polymer rubs against a transfer arm, a wafer cassette, or the like to become minute foreign matter (particle) when a wafer is being transferred, and also, in an immersion exposure process, the bevel polymer is, for example, spread over a surface of the wafer to cause defects, resulting in adversely affecting the quality of semiconductor devices.
Examples of publications describing prior arts related to a method or an apparatus for detecting such foreign matter attached to a semiconductor substrate include Japanese Laid-open Patent Publication (Kokai) No. 2007-273947.
In Japanese Laid-open Patent Publication (Kokai) No. 2007-273947, a substrate surface checking method is described in which a wafer W to which a particle P having a particle diameter of about 30 μm is attached is rapidly cooled to, for example, −20° C. or less so as to bring moisture in an atmosphere surrounding the wafer W into a supercooled state, the supercooled water is made to become attached to a periphery of the particle P on the surface of the wafer W, then the supercooled water is released from the supercooled state and thus coagulated to grow into an ice crystal around the particle P, and the particle P on the surface of the wafer W is indirectly detected by detecting the ice crystal.
According to the invention described in Japanese Laid-open Patent Publication (Kokai) No. 2007-273947, the ice crystal is grown around the particle of a minute size below the detection limit of a measuring instrument so as to increase the apparent size of the particle, and the particle P is indirectly detected by detecting the ice crystal, but no mention is made of how to detect a so-called bevel polymer attached to a peripheral edge of a substrate, which is an object of the present invention.
Here, a technique to remove a bevel polymer using, for example, ozone or laser light is under research or development, but not only management of the bevel polymer but also detection itself of the bevel polymer is difficult because the bevel polymer is of a minute size, and a peripheral edge of a substrate to which the bevel polymer is attached is a curved surface, and an effective bevel polymer detecting method has thus not been established.